1. Field of the Invention
The present invention relates generally to communications, and, more particularly, to a method and apparatus for locating a synchronization signal in a communications device, such as a cordless telephone, for example.
2. Description of the Related Art
The telecommunications industry has undergone explosive growth over the past several years. A significant contribution to this growth has been the high demand for radio communication services, such as cordless telephone service, for example. Cordless telephones provide a greater flexibility to a user than traditional landline phones by allowing them to move freely, and not tethered to the landline telephone system.
A typical cordless telephone system includes a handset unit and a base unit. The base unit is coupled to a telephone line and includes an antenna, a transmitter, and a receiver for communicating via radio frequencies with the handset unit. A local power line generally supplies the power for the base unit. The handset unit includes a speaker and a microphone, and also an antenna, a transmitter and a receiver for likewise communications with the base unit. Typically, the handset unit is powered by at least one battery. This battery is usually charged by the local power line when the handset unit is placed inside a cradle of the base unit.
Under typical operating conditions, a user generally removes the handset unit from the base unit to make calls. The user is able to roam freely about the location to make and receive calls, as long as the user stays within the generally transmitting and receiving range of the base unit. If a user desires to place a call using the handset unit, the transmitter in the handset unit generates a synchronization signal that is transmitted to the base unit. Upon receipt and detection of the synchronization signal, the base unit connects to the telephone lines and passes the voice/data signals received from the handset unit within a given channel to the telephone line. If an incoming telephone ringing signal is sensed by the base unit, reflecting an incoming call, the base unit, in turn, transmits a synchronization signal to the handset unit where it is detected by the receiver of the handset unit.
The handset unit during a standby mode (i.e., not in actual use) periodically powers-up and scans the channel range for incoming calls from the base unit. The duration of the scan cycle is one factor that determines the power consumption from the battery during standby, and therefore sets the total time the handset unit may be out of the cradle before recharging is needed.
Scanning for incoming calls is generally accomplished by programming the receiver in the handset for a specific channel frequency, waiting for a period of time to determine the presence or absence of a known synchronization signal, and sequentially stepping through the remaining channels. Thus, the receiver of the handset must generally tune to and dwell upon all the channels to look for an incoming call from the base unit. However, the above described method of sequentially scanning for the synchronization signal through all the channels may sometimes prove to be inefficient, resulting in more power consumption from the battery while the handset unit is in the standby mode.
The present invention is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.